"Good" Brown Fat Linked to Exercise.

• Position: METABOLISM

The power of exercise to boost metabolism could arise from a fat molecule with an unexpected source. In a study led by Kristin Stanford of Ohio State University, Columbus, a lipid released from fat, or lipokine, produced by brown fat was shown to surge in the bloodstream after exercise. Laurie Goodyear of Harvard Medical School, Cambridge, Mass., was the colead author of the study.

Brown fat sets itself apart from ordinary white fat in its ability to generate heat. It is what keeps hibernating bears warm and it is known to be a powerful calorie burner. Some call it "good fat."

Scientists previously thought brown fat was only in human babies, who benefit from its warming nature but, in recent years, brown fat has been recognized as a small part of adult fat stores, and become a focus of researchers seeking a better understanding of metabolism.

The researchers found a consistent pattern of increasing levels of a lipokine called 12, 13-diHOME postexercise. That fat molecule previously had been linked to exposure to cold temperatures.

"We know that exercise is great for metabolism, but we don't fully understand why that is on a cellular level. This study shows that burning of brown fat and this lipid in particular likely play an important role," says Stanford, assistant professor of physiology and cell biology.

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